Retention time reduced by 75%

[tom jupille]

So is my assumption correct?

It certainly looks like a pumping system failure!

If so, how can the problem be fixed?

Depends on what kind of system you have. One general possibility is that it's a failure of the controller (electronics? software?).

If it's a "two-pump" (also called "high-pressure-mixing" system, the problem could be a failure of the "B" (strong solvent) pump (lost prime? check valve problem?), although in that case I would expect to see t0 shift by 20%.

If it's a "one-pump" (also called "low-pressure-mixing" system, the problem is most likely a malfunctioning proportioning valve.

Your best bet would be to contact the manufacturer and get qualification test procedures to track down the problem.

[Bruce Hamilton]

I'm a little confused. I assume the column is not present ( mention of Void volume indicates it may be )?. If it is, maybe the use of 99-100% water is going to give you some issues.

Failing dramatically after a few runs, when the eluant flow rate is presumably still OK, definitely suggests that the pump is misbehaving. If the flow is not consistent, it's also likely to be the pump - assuming all solvent filters are clean and OK.

Seems like a good service is required, as suggested by Tom.

Please keep having fun,

Bruce Hamilton

[Pragmatist3]

Are you on an instrument where you can also monitor and collect pressure data? If you can, collect that data. The profile generated should be the classic drop in pressure with an increase in organic over the course of your run and all injections should look identical. When you have an aberrant RT look at the profile of the pressure for that sample. I would be willing to bet that it too will be aberrant.

Differences in how you prepare or filter your mobile phase may affect your organic conc and RT but it still should settle in and give you a constant RT with either one.

I would expect your problem is flow related and that is affecting your retention. The fact your run is long is also magnifying the problem.

If you are having something periodically blocking or restricting your flow while your analyte is moving through your stationary phase it will somewhat pause and smear leaving you with poor peak symmetry and possbile split peaks.